def where(s,c):
    '''Given string s and single-character string c, return the
    position of the first occurrence of c in s.  If c is not in s,
    return -1.'''  

    # Do not use any string methods, but you can use functions in __builtins__

def every_ith(l,i):
    '''Given list l and int i > 0, return a new list that contains every ith element
       of l, starting with index 0.'''

    # You can assume that i is > 0.  You don't need to perform error checking on that.
    
def duplicates(l):
    '''Return True if list l contains adjacent elements with the same
    value, and False otherwise'''

    # Use a while loop rather than a for-loop 

if __name__ == '__main__':
    print where("abcdeddw x",'d'), "sb", 3
    print where("a",'a'), "sb", 0
    print where("abcdeddw x",'x'), "sb", 9
    print where("abcdeddw x",'z'), "sb", -1
    print where("",'z'), "sb", -1 

    print every_ith([10,11,12,13,14,15,16,17],3), "sb", [10,13,16]
    print every_ith([10,11,12,13,14,15,16,17],10), "sb", [10]
    print every_ith([],2), "sb", []
    print every_ith([1,2,3],1), "sb", [1,2,3]

    # You decide on a good set of test cases here for duplicates